Political realism refuses to identify the moral aspirations of a particular nation with the moral laws that govern the universe. As it distinguishes … - Hans Morgenthau

However much the theory of political realism may have been misunderstood and misinterpreted, there is no gainsaying its distinctive intellectual and moral attitude to matters political. Intellectually, the political realist maintains the autonomy of the political sphere, as the economist, the lawyer, the moralist maintain theirs. He thinks in terms of interest defined as power, as the economist thinks in terms of interest defined as wealth; the lawyer, of the conformity of action with legal rules; the moralist, of the conformity of action with moral principles. The economist asks: "How does this policy affect the wealth of society, or a segment of it?" The lawyer asks: "Is this policy in accord with the rules of law?" The moralist asks: "Is this policy in accord with moral principles?" And the political realist asks: "How does this policy affect the power of the nation?" (Or of the federal government, of Congress, of the party, of agriculture, as the case may be.) The political realist is not unaware of the existence and relevance of standards of thought other than political ones. As political realist, he cannot but subordinate these other standards to those of politics.

Realism maintains that universal moral principles cannot be applied to the actions of states in their abstract universal formulation, but that they must be filtered through the concrete circumstances of time and place. The individual may say for himself: "Fiat justitia, pereat mundus (Let justice be done, even if the world perish)," but the state has no right to say so in the name of those who are in its care. Both individual and state must judge political action by universal moral principles, such as that of liberty. Yet while the individual has a moral right to sacrifice himself in defense of such a moral principle, the state has no right to let its moral disapprobation of the infringement of liberty get in the way of successful political action, itself inspired by the moral principle of national survival.

We must distinguish between military and political power. Political power is a psychological relation between those who exercise it and those over whom it is exercised. It gives the former control over certain actions of the latter through the influence which the former exert over the latter's minds. That influence may be exerted through orders, threats, persuasion, or a combination of any of these.